/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.noear.solon.configurationprocessor.json;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

// Note: this class was written without inspecting the non-free org.json source code.

/**
 * Implements {@link JSONObject#toString} and {@link JSONArray#toString}. Most application
 * developers should use those methods directly and disregard this API. For example:<pre>
 * JSONObject object = ...
 * String json = object.toString();</pre>
 * <p>
 * Stringers only encode well-formed JSON strings. In particular:
 * <ul>
 * <li>The stringer must have exactly one top-level array or object.
 * <li>Lexical scopes must be balanced: every call to {@link #array} must have a matching
 * call to {@link #endArray} and every call to {@link #object} must have a matching call
 * to {@link #endObject}.
 * <li>Arrays may not contain keys (property names).
 * <li>Objects must alternate keys (property names) and values.
 * <li>Values are inserted with either literal {@link #value(Object) value} calls, or by
 * nesting arrays or objects.
 * </ul>
 * Calls that would result in a malformed JSON string will fail with a
 * {@link JSONException}.
 * <p>
 * This class provides no facility for pretty-printing (ie. indenting) output. To encode
 * indented output, use {@link JSONObject#toString(int)} or
 * {@link JSONArray#toString(int)}.
 * <p>
 * Some implementations of the API support at most 20 levels of nesting. Attempts to
 * create more than 20 levels of nesting may fail with a {@link JSONException}.
 * <p>
 * Each stringer may be used to encode a single top level value. Instances of this class
 * are not thread safe. Although this class is nonfinal, it was not designed for
 * inheritance and should not be subclassed. In particular, self-use by overrideable
 * methods is not specified. See <i>Effective Java</i> Item 17, "Design and Document or
 * inheritance or else prohibit it" for further information.
 */
public class JSONStringer {

    /**
     * The output data, containing at most one top-level array or object.
     */
    final StringBuilder out = new StringBuilder();
    /**
     * Unlike the original implementation, this stack isn't limited to 20 levels of
     * nesting.
     */
    private final List<Scope> stack = new ArrayList<>();
    /**
     * A string containing a full set of spaces for a single level of indentation, or null
     * for no pretty printing.
     */
    private final String indent;

    public JSONStringer() {
        this.indent = null;
    }

    JSONStringer(int indentSpaces) {
        char[] indentChars = new char[indentSpaces];
        Arrays.fill(indentChars, ' ');
        this.indent = new String(indentChars);
    }

    /**
     * Begins encoding a new array. Each call to this method must be paired with a call to
     * {@link #endArray}.
     *
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer array() throws JSONException {
        return open(Scope.EMPTY_ARRAY, "[");
    }

    /**
     * Ends encoding the current array.
     *
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer endArray() throws JSONException {
        return close(Scope.EMPTY_ARRAY, Scope.NONEMPTY_ARRAY, "]");
    }

    /**
     * Begins encoding a new object. Each call to this method must be paired with a call
     * to {@link #endObject}.
     *
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer object() throws JSONException {
        return open(Scope.EMPTY_OBJECT, "{");
    }

    /**
     * Ends encoding the current object.
     *
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer endObject() throws JSONException {
        return close(Scope.EMPTY_OBJECT, Scope.NONEMPTY_OBJECT, "}");
    }

    /**
     * Enters a new scope by appending any necessary whitespace and the given bracket.
     *
     * @param empty       any necessary whitespace
     * @param openBracket the open bracket
     * @return this object
     * @throws JSONException if processing of json failed
     */
    JSONStringer open(Scope empty, String openBracket) throws JSONException {
        if (this.stack.isEmpty() && this.out.length() != 0) {
            throw new JSONException("Nesting problem: multiple top-level roots");
        }
        beforeValue();
        this.stack.add(empty);
        this.out.append(openBracket);
        return this;
    }

    /**
     * Closes the current scope by appending any necessary whitespace and the given
     * bracket.
     *
     * @param empty        any necessary whitespace
     * @param nonempty     the current scope
     * @param closeBracket the close bracket
     * @return the JSON stringer
     * @throws JSONException if processing of json failed
     */
    JSONStringer close(Scope empty, Scope nonempty, String closeBracket) throws JSONException {
        Scope context = peek();
        if (context != nonempty && context != empty) {
            throw new JSONException("Nesting problem");
        }

        this.stack.remove(this.stack.size() - 1);
        if (context == nonempty) {
            newline();
        }
        this.out.append(closeBracket);
        return this;
    }

    /**
     * Returns the value on the top of the stack.
     *
     * @return the scope
     * @throws JSONException if processing of json failed
     */
    private Scope peek() throws JSONException {
        if (this.stack.isEmpty()) {
            throw new JSONException("Nesting problem");
        }
        return this.stack.get(this.stack.size() - 1);
    }

    /**
     * Replace the value on the top of the stack with the given value.
     *
     * @param topOfStack the scope at the top of the stack
     */
    private void replaceTop(Scope topOfStack) {
        this.stack.set(this.stack.size() - 1, topOfStack);
    }

    /**
     * Encodes {@code value}.
     *
     * @param value a {@link JSONObject}, {@link JSONArray}, String, Boolean, Integer,
     *              Long, Double or null. May not be {@link Double#isNaN() NaNs} or
     *              {@link Double#isInfinite() infinities}.
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer value(Object value) throws JSONException {
        if (this.stack.isEmpty()) {
            throw new JSONException("Nesting problem");
        }

        if (value instanceof JSONArray) {
            ((JSONArray) value).writeTo(this);
            return this;
        } else if (value instanceof JSONObject) {
            ((JSONObject) value).writeTo(this);
            return this;
        }

        beforeValue();

        if (value == null || value instanceof Boolean || value == JSONObject.NULL) {
            this.out.append(value);

        } else if (value instanceof Number) {
            this.out.append(JSONObject.numberToString((Number) value));

        } else {
            string(value.toString());
        }

        return this;
    }

    /**
     * Encodes {@code value} to this stringer.
     *
     * @param value the value to encode
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer value(boolean value) throws JSONException {
        if (this.stack.isEmpty()) {
            throw new JSONException("Nesting problem");
        }
        beforeValue();
        this.out.append(value);
        return this;
    }

    /**
     * Encodes {@code value} to this stringer.
     *
     * @param value a finite value. May not be {@link Double#isNaN() NaNs} or
     *              {@link Double#isInfinite() infinities}.
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer value(double value) throws JSONException {
        if (this.stack.isEmpty()) {
            throw new JSONException("Nesting problem");
        }
        beforeValue();
        this.out.append(JSONObject.numberToString(value));
        return this;
    }

    /**
     * Encodes {@code value} to this stringer.
     *
     * @param value the value to encode
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer value(long value) throws JSONException {
        if (this.stack.isEmpty()) {
            throw new JSONException("Nesting problem");
        }
        beforeValue();
        this.out.append(value);
        return this;
    }

    private void string(String value) {
        this.out.append("\"");
        for (int i = 0, length = value.length(); i < length; i++) {
            char c = value.charAt(i);

            /*
             * From RFC 4627, "All Unicode characters may be placed within the quotation
             * marks except for the characters that must be escaped: quotation mark,
             * reverse solidus, and the control characters (U+0000 through U+001F)."
             */
            switch (c) {
                case '"':
                case '\\':
                case '/':
                    this.out.append('\\').append(c);
                    break;
                case '\t':
                    this.out.append("\\t");
                    break;
                case '\b':
                    this.out.append("\\b");
                    break;
                case '\n':
                    this.out.append("\\n");
                    break;
                case '\r':
                    this.out.append("\\r");
                    break;
                case '\f':
                    this.out.append("\\f");
                    break;
                default: {
                    if (c <= 0x1F) {
                        this.out.append(String.format("\\u%04x", (int) c));
                    } else {
                        this.out.append(c);
                    }
                }
            }

        }
        this.out.append("\"");
    }

    private void newline() {
        if (this.indent == null) {
            return;
        }

        this.out.append("\n");
        for (int i = 0; i < this.stack.size(); i++) {
            this.out.append(this.indent);
        }
    }

    /**
     * Encodes the key (property name) to this stringer.
     *
     * @param name the name of the forthcoming value. May not be null.
     * @return this stringer.
     * @throws JSONException if processing of json failed
     */
    public JSONStringer key(String name) throws JSONException {
        if (name == null) {
            throw new JSONException("Names must be non-null");
        }
        beforeKey();
        string(name);
        return this;
    }

    /**
     * Inserts any necessary separators and whitespace before a name. Also adjusts the
     * stack to expect the key's value.
     *
     * @throws JSONException if processing of json failed
     */
    private void beforeKey() throws JSONException {
        Scope context = peek();
        if (context == Scope.NONEMPTY_OBJECT) { // first in object
            this.out.append(',');
        } else if (context != Scope.EMPTY_OBJECT) { // not in an object!
            throw new JSONException("Nesting problem");
        }
        newline();
        replaceTop(Scope.DANGLING_KEY);
    }

    /**
     * Inserts any necessary separators and whitespace before a literal value, inline
     * array, or inline object. Also adjusts the stack to expect either a closing bracket
     * or another element.
     *
     * @throws JSONException if processing of json failed
     */
    private void beforeValue() throws JSONException {
        if (this.stack.isEmpty()) {
            return;
        }

        Scope context = peek();
        if (context == Scope.EMPTY_ARRAY) { // first in array
            replaceTop(Scope.NONEMPTY_ARRAY);
            newline();
        } else if (context == Scope.NONEMPTY_ARRAY) { // another in array
            this.out.append(',');
            newline();
        } else if (context == Scope.DANGLING_KEY) { // value for key
            this.out.append(this.indent == null ? ":" : ": ");
            replaceTop(Scope.NONEMPTY_OBJECT);
        } else if (context != Scope.NULL) {
            throw new JSONException("Nesting problem");
        }
    }

    /**
     * Returns the encoded JSON string.
     * <p>
     * If invoked with unterminated arrays or unclosed objects, this method's return value
     * is undefined.
     * <p>
     * <strong>Warning:</strong> although it contradicts the general contract of
     * {@link Object#toString}, this method returns null if the stringer contains no data.
     *
     * @return the encoded JSON string.
     */
    @Override
    public String toString() {
        return (this.out.length() == 0) ? null : this.out.toString();
    }

    /**
     * Lexical scoping elements within this stringer, necessary to insert the appropriate
     * separator characters (i.e. commas and colons) and to detect nesting errors.
     */
    enum Scope {

        /**
         * An array with no elements requires no separators or newlines before it is
         * closed.
         */
        EMPTY_ARRAY,

        /**
         * An array with at least one value requires a comma and newline before the next
         * element.
         */
        NONEMPTY_ARRAY,

        /**
         * An object with no keys or values requires no separators or newlines before it
         * is closed.
         */
        EMPTY_OBJECT,

        /**
         * An object whose most recent element is a key. The next element must be a value.
         */
        DANGLING_KEY,

        /**
         * An object with at least one name/value pair requires a comma and newline before
         * the next element.
         */
        NONEMPTY_OBJECT,

        /**
         * A special bracketless array needed by JSONStringer.join() and
         * JSONObject.quote() only. Not used for JSON encoding.
         */
        NULL

    }

}
